1. Field of the Invention
This invention relates to novel halogen-containing ester compounds which can take a stable thermotropic liquid crystal state and can be utilized as a liquid crystalline material useful for use in optoelectronics related elements using a liquid crystal and electrochemichromism such as display for liquid crystal television receiver, optical printer head, opto-Fourier transform element, light valve and the like, their intermediates and method of producing the same as well as liquid crystal compositions containing the above compounds and light switching elements using the same.
2. Related Art Statement
Liquid crystalline compounds having asymmetric carbon in their molecule can take a chiralsmectic phase in the crystal structure and may exhibit properties as a ferroelectric liquid crystal having a fast response time, so that they are recently expected as a liquid crystalline material for displaying means requiring a high speed responsibility. As such a liquid crystalline compound, there have been proposed optically active halocarboxylic acid derivatives (Japanese Patent laid open No. 61-165350), ether compounds containing optical active group and halogen-containing phenylbiphenyl ester group (Japanese Patent laid open No. 61-210056), ester compounds containing optical active group and phenylbiphenyl ester group (Japanese Patent laid open No. 60-32748) and so on.
As properties required in the ferroelectric liquid crystalline material, there are various requirements that the chiralsmectic C phase is exhibited over a wide temperature range inclusive of room temperature, the spontaneous polarization is large, the material is chemically stable and the like. Since these requirements are very difficult to be satisfied only by the single compound, the requirements as a liquid crystalline composition are usually satisfied by mixing some compounds.
On the other hand, the light switching element is an element for switching on and off light in accordance with external force such as electric field, magnetic field or the like. At the present, twisted nematic (TN) type system consisting of nematic liquid crystal is exclusively used as this type of the light switching element in the field for displaying elements. However, the switching element using the nematic liquid crystal has a drawback that the response is slow. Therefore, the elements using the ferroelectric liquid crystal are proposed as a light switching element having a fast responsibility instead of the nematic liquid crystal.
The halocarboxylic acid derivatives are relatively large in the spontaneous polarization, but are lacking in the light stability because they have generally carbon-halogen bond and also the temperature range showing the ferroelectricity is narrow. Furthermore, the ether compounds containing the optical active group are lacking in the light stability because of the presence of halogen, relatively large in the spontaneous polarization but narrow in the temperature range showing the ferroelectricity. Moreover, the ester compounds containing the optical active group are relatively wide in the temperature range showing the ferroelectricity, but are small in the spontaneous polarization.
That is, the liquid crystalline materials used for displaying means requiring high speed responsibility are required to have properties that the spontaneous polarization is large, the viscosity is low, the chiralsmectic C phase is exhibited over a wide temperature range inclusive of room temperature and the like. However, materials sufficiently satisfying these properties are not yet provided at the present.
Further, it is attempted to stabilize the chiralsmectic C phase by introducing halogen into a nucleus portion of the liquid crystal, or to prevent the appearance of higher smectic phase at a low temperature side of chiralsmectic phase (Saito et al, 13th Panel Discussion of Liquid Crystal1Z06; Shoji et al, 13th Panel Discussion of Liquid Crystal 1Z13). In this case, however, the displaying elements having a sufficient high speed responsibility can not be manufactured even by using such liquid crystalline materials.
On the contrary, the inventors have previously found that compounds having an asymmetric carbon at .alpha.-position and ketone group directly bonded to benzene ring in molecule are stable against light or the like and wide in the temperature range enantiotropically forming a liquid crystalline state, and particularly when optical activity is given to the asymmetric carbon, they are rendered into a ferroelectric liquid crystal exhibiting chiralsmectic C phase and having a large spontaneous polarization and a fast response rate (International Publication No. WO88/07518).